NOTE: As their name suggests hints are not exactly Aliens: Colonial Marines cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing Aliens: Colonial Marines even more entertaining.

Steam Achievements
... But No Cigar: Rescue a teammate from a Close Encounter
Adaptive Morphology: Upgrade every Appearance slot once for a Xenomorph class
Adios, Muchachos: Gib two enemies at once
Another Bug Hunt: Complete a Challenge
Another Day in the Corps: Complete Distress
Anytime, Anywhere: Kill a Crusher without it damaging you
Arbitrarily Exterminated: Kill 2179 Xenomorphs
Bad Feeling About This Drop: Complete Sulaco Falls
Coming Outta the Walls!: Kill a Xenomorph climbing on the walls or ceiling
Distinguished Service Medal: Complete all Challenges
Don't Count Me Out: Revive a teammate
Dragged Queen: Complete Home
Easter Egg: Find the Easter Egg
Eat This!: Kill a Xenomorph with a shotgun at very close range
Entry Prohibited: Kill 10 Xenomorphs that are using vents
Field Modified, Kill Certified: Upgrade every slot for a weapon
Field Promotion: Earn Rank 2 as a Marine
Fire Drill: Arm the emergency release and escape in under 2:30 on Sulaco Falls
Game Over, Man!: Complete all Campaign levels on any difficulty
Heavy Lifting: Defeat the Raven in under 1:10 on Soldier difficulty or higher
I Can Handle Myself: Purchase all Upgrades for a weapon
I Feel Safer Already: Have another player join your party
I Heard THAT: Collect all 12 Audio LogsI Like to Keep These Handy: Collect all 6 Legendary Weapons
I Love the Corps!: Earn Rank 60 as a Marine
It's a Dry Heat: Kill 3 enemies with a single U4 Firebomb
Just a Grunt: Complete Hope in Hadley's
Lean and Mean: Earn Rank 20 as a Marine
Let's Rock!: Kill 10 Xenomorphs in a game with the M56A2 Smart Gun
Love at First Sight: Survive a Close Encounter with a Facehugger
Majority Shareholder: Spend 30 Commendations
Micro Changes in Air Density: Track 100 hostile targets with the Motion Tracker
Mostly Come at Night…: Find Newt's doll
Need a Deck Of Cards?: Set up a UA 571-C Remote Sentry
No Need For Alarm: Complete One Bullet without setting off the alarm
No Offense: Melee a Lurker that is pouncing towards you
Not Bad For a Human: Complete all Campaign levels on Hardened difficulty
Oorah to Ashes: Collect a Dog Tag
Perfect Killing Machine: Upgrade every Loadout slot for a Xenomorph class
Personal Friend of Mine: Collect a Legendary Weapon
Quoth the Raven: Complete The Raven
Ready to Fry Half a City: Edit a Marine Loadout
Remember the Fallen: Collect all 35 Dog Tags
Secreted from What?: Kill 5 Spitters without being damaged by acid
Short, Controlled Bursts: Defeat all Xenomorphs in the Sulaco hanger bay without them crossing your barricade
State of the Badass Art: Complete all Campaign levels on Ultimate Badass difficulty
Stay Frosty: Complete an entire Challenge category
Still Got a Job to Do: Complete Rampart
Structural Perfection: Edit a Xenomorph Loadout
You Look Just Like I Feel: Upgrade every Appearance slot once for your Marine